socket: finish constant to Enum/Flag conversion

GitHub fields:

assignee = 'https://github.com/ethanfurman'
closed_at = None
created_at = <Date 2016-09-11.20:34:18.544>
labels = ['type-feature']
title = 'socket: finish constant to Enum/Flag conversion'
updated_at = <Date 2016-09-12.03:08:43.398>
user = 'https://github.com/ethanfurman'

bugs.python.org fields:

activity = <Date 2016-09-12.03:08:43.398>
actor = 'ethan.furman'
assignee = 'ethan.furman'
closed = False
closed_date = None
closer = None
components = []
creation = <Date 2016-09-11.20:34:18.544>
creator = 'ethan.furman'
dependencies = []
files = ['44567']
hgrepos = []
issue_num = 28083
keywords = ['patch']
message_count = 8.0
messages = ['275851', '275852', '275854', '275867', '275868', '275870', '275902', '275931']
nosy_count = 5.0
nosy_names = ['christian.heimes', 'ned.deily', 'ethan.furman', 'python-dev', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'commit review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue28083'
versions = ['Python 3.6']